Being able to predict conception chance by a simple method for the sperm of all animals would be extremely useful in terms of both cost and labor. In the case of livestock, for example, since it is necessary to obtain offspring through efficient conception, it is important to provide semen for which fertility is guaranteed. From this viewpoint, there is a desire to develop a method for evaluating the quality of sperm that accurately reflects fertility.
With respect to cattle breeding, for example, although the proliferation of artificial insemination in Japan is nearly 100%, the resulting conception rate is decreasing each year. Among dairy breeds, although the conception rate after first insemination was 62.4% and the conception rate after 1 to 3 inseminations was 62.0% in 1989, the conception rate after first insemination had decreased to 45.6% and the conception rate after 1 to 3 inseminations had decreased to 44.4% in 2011, (Non-Patent Document 1: Livestock Improvement Association of Japan, Inc., 2011 Conception Survey Results (2013)). Under the present circumstances in which conception rate is exhibiting a decreasing trend in this manner, the providing of semen for which fertility is guaranteed would be extremely useful from the viewpoint of production efficiency.
Conventionally, inspection of sperm quality has focused primarily on such factors as sperm viability, sperm motility rate, sperm motility retention rate, mitochondria normal rate, acrosome normal rate or sperm morphology normal rate (Patent Document 1: Japanese Patent No. 5092149, Non-Patent Document 2: Rodriguez-Martinez H., Reprod. Domest. Anim. 41, Suppl. 2, 2-10 (2006)). However, the correlations between these inspection methods and conception chance have not necessarily been high for all parameters, thereby preventing these inspection methods from serving as simple indicators reflective of fertility relative to sperm. The cause of the lack of a high correlation between these inspection methods and fertility is thought to be because these methods do not reflect sperm behavior in the female body or the environment at the time of fertilization.
Once sperm has reached the ampulla of the fallopian tube, motility increases prominently when the female ovulates, and sperm that exhibits hyperactivated motility is thought to result in successful conception (Non-Patent Document 3: Suarez, S. S., Int. J. Dev. Biol. 52 (5-6), 455-62 (2008)). Therefore, an inspection method has been proposed that reflects actual conditions inside the female body (Non-Patent Document 4: Hamano, et al, Journal of the Hokuriku Branch of the Japan Society of Animal Science 81, 63-68 (2000)). In addition, inspections can also be carried out using an in vitro fertilization test in which sperm is actually made to fertilize an egg.